arXiv subjects

K. Kirch

Publications and source records attributed to K. Kirch.

At least 73 records · Page 4Linked to original sources

arXiv2018

Demonstration of sensitivity increase in mercury free-spin-precession magnetometers due to laser-based readout for neutron electric dipole moment searches

We report on a laser based $^{199}$Hg co-magnetometer deployed in an experiment searching for a permanent electric dipole moment of the neutron. We demonstrate a more than five times increased signal to-noise-ratio in a direct comparison measurement with its $^{204}$Hg discharge bulb-based predecessor. An improved data model for the extraction of important system parameters such as the degrees of absorption and polarization is derived. Laser- and lamp-based data-sets can be consistently described by the improved model which permits to compare measurements using the two different light sources and to explain the increase in magnetometer performance. The laser-based magnetometer satisfies the magnetic field sensitivity requirements for the next generation nEDM experiments.

physics.ins-det↗

arXiv2017

A simple method of coil design

In this article we present a method to design a coil producing an arbitrarily shaped magnetic field by restricting the path of the coil's wires to a regular grid. The solution is then found by a simple least squares minimum. We discuss practical applications, in particular in the active magnetic field stabilization system of the neutron electric dipole moment experiment at the Paul Scherrer Institute in Villigen, Switzerland. We also publish the software implementation of the method.

physics.ins-det↗

arXiv2017

High-power closed-cycle $^4$He cryostat with top-loading sample exchange

We report on the development of a versatile cryogen-free laboratory cryostat based upon a commercial pulse tube cryocooler. It provides enough cooling power for continuous recondensation of circulating $^4$He gas at a condensation pressure of approximately 250~mbar. Moreover, the cryostat allows for exchange of different cryostat-inserts as well as fast and easy "wet" top-loading of samples directly into the 1 K pot with a turn-over time of less than 75~min. Starting from room temperature and using a $^4$He cryostat-insert, a base temperature of 1.0~K is reached within approximately seven hours and a cooling power of 250~mW is established at 1.24~K.

physics.ins-det↗

arXiv2017

Search for axion-like dark matter through nuclear spin precession in electric and magnetic fields

We report on a search for ultra-low-mass axion-like dark matter by analysing the ratio of the spin-precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms for an axion-induced oscillating electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range $10^{-24}~\textrm{eV} \le m_a \le 10^{-17}~\textrm{eV}$. Our null result sets the first laboratory constraints on the coupling of axion dark matter to gluons, which improve on astrophysical limits by up to 3 orders of magnitude, and also improves on previous laboratory constraints on the axion coupling to nucleons by up to a factor of 40.

hep-ph↗

arXiv2017

The proton radius puzzle

High-precision measurements of the proton radius from laser spectroscopy of muonic hydrogen demonstrated up to six standard deviations smaller values than obtained from electron-proton scattering and hydrogen spectroscopy. The status of this discrepancy, which is known as the proton radius puzzle will be discussed in this paper, complemented with the new insights obtained from spectroscopy of muonic deuterium.

physics.atom-ph↗

arXiv2017

High efficiency cyclotron trap assisted positron moderator

We report the realisation of a cyclotron trap assisted positron tungsten moderator for the conversion of positrons with a broad keV- few MeV energy spectrum to a mono-energetic eV beam with an efficiency of 1.8(2)% defined as the ratio of the slow positrons divided by the $β^+$ activity of the radioactive source. This is an improvement of almost two orders of magnitude compared to the state of the art of tungsten moderators. The simulation validated with this measurement suggests that using an optimised setup even higher efficiencies are achievable.

physics.ins-det↗

arXiv2016

Comparison of ultracold neutron sources for fundamental physics measurements

Ultracold neutrons (UCNs) are key for precision studies of fundamental parameters of the neutron and in searches for new CP violating processes or exotic interactions beyond the Standard Model of particle physics. The most prominent example is the search for a permanent electric dipole moment of the neutron (nEDM). We have performed an experimental comparison of the leading UCN sources currently operating. We have used a 'standard' UCN storage bottle with a volume of 32 liters, comparable in size to nEDM experiments, which allows us to compare the UCN density available at a given beam port.

physics.ins-det↗

arXiv2016

Spatial confinement of muonium atoms

We report the achievement of spatial confinement of muonium atoms (the bound state of a positive muon and an electron). Muonium emitted into vacuum from mesoporous silica reflects between two SiO$_2$ confining surfaces separated by 1 mm. From the data, one can extract that the reflection probability on the confining surfaces kept at 100 K is about 90% and the reflection process is well described by a cosine law. This technique enables new experiments with this exotic atomic system and is a very important step towards a measurement of the 1S-2S transition frequency using continuous wave laser spectroscopy.

physics.atom-ph↗

arXiv2016

Ultracold neutron detection with 6Li-doped glass scintillators, NANOSC: a fast ultracold neutron detector for the nEDM experiment at the Paul Scherrer Institute

This paper summarizes the results from measurements aiming to characterize ultracold neutron detection with 6Li-doped glass scintillators. Single GS10 or GS20 scintillators, with a thickness of 100-200 micrometer, fulfill the ultracold neutron detection requirements with an acceptable neutron-gamma discrimination. This discrimination is clearly improved with a stack of two scintillators: a 6Li-depleted glass bonded to a 6Li-enriched glass. The optical contact bonding is used between the scintillators in order to obtain a perfect optical contact. The scintillator's detection efficiency is similar to that of a 3He Strelkov gas detector. Coupled to a digital data acquisition system, counting rates up to a few 10^5 counts/s can be handled. A detector based on such a scintillator stack arrangement was built and has been used in the neutron electric dipole moment experiment at the Paul Scherrer Institute since 2010. Its response for the regular runs of the neutron electric dipole moment experiment is presented.

physics.ins-det↗

arXiv2016

An ultracold neutron storage bottle for UCN density measurements

We have developed a storage bottle for ultracold neutrons (UCN) in order to measure the UCN density at the beamports of the Paul Scherrer Institute's (PSI) UCN source. This paper describes the design, construction and commissioning of the robust and mobile storage bottle with a volume comparable to typical storage experiments 32 liter e.g. searching for an electric dipole moment of the neutron.

physics.ins-det↗

arXiv2016

Multi-pass oscillator layout for high-energy mode-locked thin-disk lasers

A novel optical layout for a multi-pass resonator is presented paving the way for pulse energy scaling of mode-locked thin-disk lasers. The multi-pass resonator we are proposing consists of a concatenation of nearly identical optical segments. Each segment corresponds to a round-trip in an optically stable cavity containing an active medium exhibiting soft aperture effects. This scheme is apt for energy and power scaling because the stability region of this multi-pass resonator contrarily to the 4f-based schemes does not shrink with the number of passes. Simulation of the eigen-mode of this multi-segment resonator requires considering aperture effects. This has been achieved by implementing effective Gaussian apertures into the ABCD-matrix formalism as lenses with imaginary focal length. We conclude proposing a simple way to double the stability region of the state-of-the-art layouts used in industry achievable by a minimal rearrangement of the used optical components.

physics.optics↗

arXiv2015

Experiments towards resolving the proton charge radius puzzle

We review the status of the proton charge radius puzzle. Emphasis is given to the various experiments initiated to resolve the conflict between the muonic hydrogen results and the results from scattering and regular hydrogen spectroscopy.

physics.atom-ph↗

arXiv2015

A Revised Experimental Upper Limit on the Electric Dipole Moment of the Neutron

We present for the first time a detailed and comprehensive analysis of the experimental results that set the current world sensitivity limit on the magnitude of the electric dipole moment (EDM) of the neutron. We have extended and enhanced our earlier analysis to include recent developments in the understanding of the effects of gravity in depolarizing ultracold neutrons (UCN); an improved calculation of the spectrum of the neutrons; and conservative estimates of other possible systematic errors, which are also shown to be consistent with more recent measurements undertaken with the apparatus. We obtain a net result of $d_\mathrm{n} = -0.21 \pm 1.82 \times10^{-26}$ $e$cm, which may be interpreted as a slightly revised upper limit on the magnitude of the EDM of $3.0 \times10^{-26}$ $e$cm (90% CL) or $ 3.6 \times10^{-26}$ $e$cm (95% CL). This paper is dedicated by the remaining authors to the memory of Prof. J. Michael Pendlebury.

hep-ex↗

arXiv2015

A device for simultaneous spin analysis of ultracold neutrons

We report on the design and first tests of a device allowing for measurement of ultracold neutrons polarisation by means of the simultaneous analysis of the two spin components. The device was developed in the framework of the neutron electric dipole moment experiment at the Paul Scherrer Institute. Individual parts and the entire newly built system have been characterised with ultracold neutrons. The gain in statistical sensitivity obtained with the simultaneous spin analyser is $(18.2\pm6.1)\%$ relative to the former sequential analyser under nominal running conditions.

physics.ins-det↗

arXiv2015

Thin-disk laser pump schemes for large number of passes and moderate pump source quality

Novel thin-disk laser pump layouts are proposed yielding an increased number of passes for a given pump module size and pump source quality. These novel layouts result from a general scheme which bases on merging two simpler pump optics arrangements. Some peculiar examples can be realized by adapting standard commercially available pump optics simply by intro ducing an additional mirror-pair. More pump passes yield better efficiency, opening the way for usage of active materials with low absorption. In a standard multi-pass pump design, scaling of the number of beam passes brings ab out an increase of the overall size of the optical arrangement or an increase of the pump source quality requirements. Such increases are minimized in our scheme, making them eligible for industrial applications

physics.optics↗

arXiv2015

Thin-disk laser multi-pass amplifier

In the context of the Lamb shift measurement in muonic helium we developed a thin-disk laser composed of a Q-switched oscillator and a multi-pass amplifier delivering pulses of 150 mJ at a pulse duration of 100 ns. Its peculiar requirements are stochastic trigger and short delay time (< 500 ns) between trigger and optical output. The concept of the thin-disk laser allows for energy and power scaling with high efficiency. However the single pass gain is small (about 1.2). Hence a multi-pass scheme with precise mode matching for large beam waists (w = 2 mm) is required. Instead of using the standard 4f design, we have developed a multi-pass amplifier with a beam propagation insensitive to thermal lens effects and misalignments. The beam propagation is equivalent to multiple roundtrips in an optically stable resonator. To support the propagation we used an array of 2 x 8 individually adjustable plane mirrors. Astigmatism has been minimized by a compact mirror placement. Precise alignment of the kinematic array was realized using our own mirror mount design. A small signal gain of 5 for 8 passes at a pump power of 400 W was reached. The laser was running for more than 3 months without the need of realignment. Pointing stability studies is also reported here.

physics.optics↗

arXiv2015

Observation of gravitationally induced vertical striation of polarized ultracold neutrons by spin-echo spectroscopy

We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a $|B_0|=1~\text{μT}$ magnetic field. We have demonstrated that the analysis of UCN spin-echo resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCN of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of $1.1~\text{pT/cm}$. This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime.

physics.ins-det↗

arXiv2015

Gravitational Depolarization of Ultracold Neutrons: Comparison with Data

We compare the expected effects of so-called gravitationally enhanced depolarization of ultracold neutrons to measurements carried out in a spin-precession chamber exposed to a variety of vertical magnetic-field gradients. In particular, we have investigated the dependence upon these field gradients of spin depolarization rates and also of shifts in the measured neutron Larmor precession frequency. We find excellent qualitative agreement, with gravitationally enhanced depolarization accounting for several previously unexplained features in the data.

physics.ins-det↗